[Frontend] Make TIMEOUT_KEEP_ALIVE configurable through env var (#18472)

Signed-off-by: liusiqian <liusiqian@tal.com>

tests/async_engine/api_server_async_engine.py

@@ -8,6 +8,7 @@ import uvicorn
 from fastapi.responses import JSONResponse, Response
 
 import vllm.entrypoints.api_server
+import vllm.envs as envs
 from vllm.engine.arg_utils import AsyncEngineArgs
 from vllm.engine.async_llm_engine import AsyncLLMEngine
 from vllm.utils import FlexibleArgumentParser
@@ -46,9 +47,8 @@ if __name__ == "__main__":
     engine_args = AsyncEngineArgs.from_cli_args(args)
     engine = AsyncLLMEngineWithStats.from_engine_args(engine_args)
     vllm.entrypoints.api_server.engine = engine
-    uvicorn.run(
-        app,
-        host=args.host,
-        port=args.port,
-        log_level="debug",
-        timeout_keep_alive=vllm.entrypoints.api_server.TIMEOUT_KEEP_ALIVE)
+    uvicorn.run(app,
+                host=args.host,
+                port=args.port,
+                log_level="debug",
+                timeout_keep_alive=envs.VLLM_HTTP_TIMEOUT_KEEP_ALIVE)